Single handed operation is usefull for my use case as well (mainly CAD and graphic work). I've tried various approaches:

• Swap hands feature from QMK: it works, but has some limitations. I also just made a layer with swapped layout to work around some of the limitations, but ultimately I just didn't find it very convenient.
• I then proceeded to write my own "autoswap" feature, inspired by autoshift. Basically it is swap hands by holding any alpha key. So tap Q is Q, hold Q results in P. That worked brilliantly, but the compromise is that you can't use any tap-hold functions on your alphas (like layer taps or homerow mods). Since I don't like homerow mods anyway, I could manage with my 36 key layout, but it was definitely a compromise to fit all mods and layer taps on thumbs or combos. Going up to 40 keys would probably have made this a pretty decent solution though.
• Then I added a trackball to my keyboard. Having the trackball integrated still required me to move my right hand slightly away from the home row, but its much less of an issue than before, and it made any swap hands feature redundant. I definitely recommend looking into something like a Charybdis, probably the best straight out of box solution (out of box solution being relative ofc in this mad world of DIY ergo boards).
• Right now I'm experimenting with a layout inspired by TAIPO; its a chording layout, that is intended for use with 2 hands on a 20 key layout, but left and right are mirrored, so it is fully functional in one handed operation as well. Its definitely a learning curve, but I'm surprised by how natural it feels. Its like a 10 key macropad, which is somehow magically equally functional as a full keyboard, without feeling like a compromise! I definitely recommend at least reading up on it: https://inkeys.wiki/en/keymaps/taipo ; it may be a bit much to get into if you are new to ergo keyboards and small layouts though, so I would suggest first getting familiar with something like a 36-40 key split and toying around in QMK.